The British investigative journalist whose partner was detained at London's Heathrow airport for nine hours Sunday says the government's efforts to intimidate him will have the exact opposite effect.

David Michael Miranda, the 28-year-old partner of London Guardian journalist Glenn Greenwald, was detained for nine hours — the maximum time legally permitted without being charged — at London's Heathrow Airport Sunday, reportedly in connection with Section 7 of England's Terrorism Act of 2000.

But in a column in the Guardian Sunday, Greenwald posited that his partner's detainment was a move of retaliation for Greenwald's dogged reporting on the information leaked by National Security Agency contractor Edward Snowden.

"But [U.K. officials] obviously had zero suspicion that David was associated with a terrorist organization or involved in any terrorist plot," wrote Greenwald. "Instead, they spent their time interrogating him about the NSA reporting which Laura Poitras, the Guardian and I are doing, as well the content of the electronic products he was carrying."

Miranda had been in Berlin for a week visiting Poitras, a documentary filmmaker who has also been helping to disseminate the info leaked by Snowden, to assist Greenwald. It seems the Guardian paid for the trip and Miranda was on his way home to Rio de Janeiro, where he lives with Greenwald.

According to a report published by the Guardian, Miranda was released, but officials confiscated electronics equipment including his mobile phone, laptop, camera, memory sticks, DVDs, and games consoles, with no mention of when or if they would be returned.

"This is obviously a rather profound escalation of their attacks on the news-gathering process and journalism," wrote Greenwald on Sunday. "It's bad enough to prosecute and imprison sources. It's worse still to imprison journalists who report the truth. But to start detaining the family members and loved ones of journalists is simply despotic."

Because U.K. officials confiscated Miranda's phone, Greenwald said he had not spoken to his partner when he wrote Sunday's article. But he said the couple's lawyer, who did speak with Miranda immediately after he was released, said the Brazilian was in good spirits and confidently defiant.

Greenwald shared that defiance with his partner, promising that this "effort at intimidation" would only embolden his reporting.

"If the U.K. and U.S. governments believe that tactics like this are going to deter or intimidate us in any way from continuing to report aggressively on what these documents reveal, they are beyond deluded," wrote Greenwald. "If anything, it will have only the opposite effect: to embolden us even further."

The Brazilian government issued a statement expressing its "grave concern" over the detention of one of its citizens and the use of antiterror legislation, saying, "This measure is without justification since it involves an individual against whom there are no charges that can legitimate the use of that legislation," according to the Guardian. "The Brazilian government expects that incidents such as the one that happened to the Brazilian citizen [Sunday] are not repeated."